1. Field Of The Invention
The present invention generally relates to a refrigerant compressor and, more particularly, to a slant plate type compressor, such as a wobble plate type compressor, with a variable displacement mechanism suitable for use in an automotive air conditioning system.
2. Description Of The Prior Art
A wobble plate type compressor with a variable displacement mechanism suitable for use in an automotive air conditioning system is disclosed in Japanese Utility Model Application Publication No. 64-27487. The compressor is driven by the engine of the automobile.
The compressor includes a variable displacement mechanism which comprises a first communication path linking a crank chamber and a suction chamber in fluid communication, and a second communication path linking the crank chamber and a discharge chamber. A first valve control mechanism controlling the opening and closing of the first communication path is disposed within the first communication path. A second valve control mechanism controlling the opening and closing of the second communication path is disposed within the second communication path. The first communication path is provided with a first valve seat formed at one portion thereof. The second communication path is provided with a second valve seat formed at one portion thereof. The first valve control mechanism includes a first valve member which is disposed so as to be received on and moved away from the first valve seat. The second valve control mechanism includes a second valve member which is disposed so as to be received on and moved away from the second valve seat.
The first and second valve members are linked through a rod member so that when the first valve member is received on the first valve seat to close the first communication path, the second valve member is moved away from the second valve seat to open the second communication path. Conversely, when the first valve member is moved away from the first valve seat, the second valve member is received on the second valve seat.
In operation of the compressor, the capacity of the compressor depends upon the crank chamber pressure relative to the suction chamber pressure, with the compressor operating at maximum capacity when the crank and suction chambers are linked in fluid communication. When the link between the crank and suction chambers is terminated, simultaneously linking the crank and discharge chambers, the pressure in the crank chamber increases relative to the suction chamber due to the flow of high pressure fluid from the discharge chamber to the crank chamber, reducing capacity. Of course, when operating at reduced capacity, the power demands of the compressor on the engine are reduced as well.
The first valve control mechanism includes a pressure sensing device such as a diaphragm for sensing on one side the pressure in the suction chamber. The opposite side of the diaphragm is acted upon by a cylindrical member made of magnetic material and forming part of a solenoid mechanism. The relative position of the cylindrical member and thus the effective force provided thereby upon the diaphragm is controlled by the solenoid in response to an external vehicle condition, such as the power demands made upon the engine to drive the vehicle.
The diaphragm is responsive to the net force acting on the opposite sides thereof and acts upon the rod member linking the first and second valve members to simultaneously control the opening and closing of the two communication paths. For a given positioning of the cylindrical member the effect thereof on the diaphragm is constant, and the diaphragm responds to changes in the suction pressure to act upon the rod member to control the link between the crank and suction chambers. Thus, for a given positioning of the cylindrical member, the first valve member acts to maintain the suction pressure at a predetermined constant value. By changing the position of the cylindrical member through functioning of the solenoid in response to the demands made upon the engine for driving the vehicle, the predetermined constant value of the suction pressure can be changed in response to the demands made upon the engine.
As discussed above, the compressor operates at maximum capacity when the crank and suction chambers are linked. This linkage occurs when the suction pressure exceeds the predetermined constant value and acts upon the diaphragm to move the first valve member away from the first valve seat, simultaneously isolating the crank and discharge chambers. For example, when the heat load on the evaporator is great, the suction pressure will be great, causing the crank and suction chambers to be linked, maximizing capacity.
However, when the power demand for the vehicle is great, it is not desirable for the compressor to operate at maximum capacity, even if the heat load on the evaporator and the corresponding suction pressure are large. The solenoid acts in response to the greater demand for power made on the engine by the vehicle, to increase the effect of the cylindrical member upon the diaphragm, for example, by reducing the force with which the cylindrical member is pulled away from the diaphragm. Thus, the predetermined constant value at which the suction pressure is maintained will be increased, requiring an even greater pressure in the suction chamber before the crank and suction chambers will be linked.
Therefore, even if the suction pressure is increased, for example, due to an increase of the heat load on the evaporator, the compressor will not function at maximum capacity while the demand for engine power by the vehicle is large, since the crank and suction chambers will be isolated. Correspondingly, the crank and discharge chambers will be linked, rapidly increasing the crank pressure relative to the suction pressure to minimize compressor capacity. Accordingly, the energy derived from the engine of the vehicle is effectively used for driving the vehicle.
When the first valve member is received on the first valve seat so as to close the first communication path while the second valve member is moved away from the second valve seat so as to open the second communication path, the refrigerant gas at discharge pressure flows to the crank chamber, increasing the pressure therein, and quickly reducing capacity, as discussed above. The quantity of refrigerant gas which flows from the discharge chamber to the crank chamber is substantially determined by the size of the open area of the second valve seat. However, in the manufacturing process of the compressor, it is difficult to manufacture the second valve seat so as to have a certain size which allows for the controlled flow of a predetermined, known volume of the refrigerant gas from the discharge chamber to the crank chamber.
Since the volume of flow cannot be effectively controlled, when the displacement of the compressor is minimized, if the size of the open area of the second valve seat is selected to be too large, the quantity of the refrigerant gas which flows from the discharge chamber to the crank chamber is large, causing the pressure in the crank chamber to be quickly increased to thereby quickly reduce the displacement of the compressor. However, the pressure in the crank chamber may be increased to an excessively high value and maintained at that value until the crank and suction chambers are again linked, resulting in damage to the internal component parts of the compressor.
On the other hand, if the size of the open area of the second valve seat is selected to be small, the quantity of the refrigerant gas which flows from the discharge chamber to the crank chamber is small, causing the pressure in the crank chamber to be too slowly increased. Thus, even though the crank chamber pressure will not exceed and be maintained at a value which causes damage to the internal components of the compressor, the displacement of the compressor will not be reduced quickly enough to obtain an effective reduction of the power demand on the engine by the compressor during times when a large amount of engine power is required to drive the vehicle.
Further, in both of the above cases, the effectiveness of displacement control is limited by the fact that the first and second valve control mechanisms are not controlled independently. When the suction and crank chambers are isolated, the discharge and crank chambers are linked, increasing the crank chamber pressure. However, if it is desired that the crank and discharge chambers be isolated to limit the build-up of pressure in the crank chamber, the crank and suction chambers must be linked. This linkage may occur when the demand for engine power to drive the vehicle is still large. Thus, before it is desired to do so, the compressor may be restored to maximum displacement.